In this work, a study of the effect of excitation and governor on the stability of electric machines is presented. In particular, a model of a synchronous machine (in generator mode) connected to a hydraulic turbine Proportional-Integral-Derivative (PID) governor with excitation system is analyzed.

1. A PRESENTATION
ON
DYNAMIC MODELLING OF EXCITATION AND
GOVERNOR EFFECT ON STABILITY OF
ELECTRICAL MACHINES
BY
K. N. UKOIMA, P. I. OBI, C. S. EZEONYE
SEPTEMBER, 2019

2. INTRODUCTION
• An electric governor is a control device that controls the speed of an
electric machine. Its task is to keep the speed of the engine constant - to
keep the speed of the engine at a predetermined speed without being
affected by changes in the load.
• Excitation is the process of generating a magnetic field by means of an
electric current. It is important to be able to control this field because
this will in turn sustain the system voltage at a nominal value.
• Majority of the current research is mostly in excitation control.
• Many other contributions made, have been in the dynamics of
governor control.
• In this paper, we aim to complement the various studies in the
literature by studying the effects of governor and excitation on
electrical machines.
• In particular, we focus on the generator in conjunction with a
hydraulic turbine governor. Faults (three phase) were introduced into
the system and the stabilizing effects of the governor and excitation
control is shown.

3. POWER SYSTEM MODELS
1. SYNCHRONOUS MACHINE
The synchronous machine in simulink can operate in the generator or motor
modes. The mode of operation is determined by the mechanical power sign.
When the sign is positive, it operates in the generator mode. A negative sign
implies motor mode of operation.
Figure 1: Simulink synchronous machine block. Source: (Matlab, 2019)

4. GOVERNOR
Figure 2: Simulink hydraulic turbine and governor. Source: (Matlab, 2019)

5. EXCITER
The excitation system regulates the terminal voltage of the synchronous
machine in the generator mode.
Figure 3: Simulink excitation system. Source: (Matlab, 2019)

6. METHODOLOGY
The model shows a synchronous machine connected in generator mode and used in
conjunction with a hydraulic turbine governor and an excitation system. The
synchronous machine is connected to a 210kV network through a 210MVAtransformer.
Figure 4: Simulation model to study effects of governor and excitation control

7. S/No Description Values
1. Nominal power 200KVA
2. Rated phase voltage 440V
3. Initial mechanical power 48.9kW
4. Nominal frequency 50Hz
5. Rotor type Salient pole
6. Stator parameters Rs(0.26Ω), L1(1.14mH)
Lmd(13.7mH), Lmq(11mH)
7. Field parameters Rf(0.13Ω), Lf(2.1mH)
8. Friction factor 0
9. Inertia 24.9
10. Pole pairs 2
11. Preset model No preset model
Table 1: Generator parameters

8. RESULTS
Case 1: Single fault for duration t = 0.1s (starts at 0.2s and ends 0.3s)
Figure 5: Rotor speed for case 1 Figure 6: Field voltage for case 1
Figure 7: Stator current, Iq for case 1 Figure 8: Stator current, Id for case 1

9. Figure 9: Mechanical power for case 1
Figure 10: Terminal voltages, Va,b,c for case 1

10. Case 2: Single fault for duration t = 0.3s
Figure 11: Rotor speed for case 2 Figure 12: Field voltage for case 2
Figure 13: Stator current, Id for case 2 Figure 14: Stator current, Iq for case 2

11. Figure 15: Mechanical power for case 2
Figure 16: Terminal voltages, Va,b,c for case 2

12. Case 3: Multiple faults at time t = 0.2s and 1.2s – Each has a 0.1s duration
Figure 20: Rotor speed for case 3 Figure 21: Field voltage for case 3
Figure 22: Stator current, Id for case 3 Figure 23: Stator current, Iq for case 3

13. Figure 24: Mechanical power for case 3
Figure 25: Terminal voltages, Va,b,c for case 3

14. CONCLUSION
•This paper studied the effect of excitation and governor on the stability
of electric machines.
•The generator terminal voltage was restored back to its nominal value
within 2 seconds after a fault which lasts for 0.1seconds occurs.
•For extended fault duration of 0.3 seconds, the terminal voltage was
stabilized within 5 seconds.
•Other system parameters such as the rotor speed, field voltages, stator
currents and the mechanical input power were all restored back to their
steady state values within 8 seconds after the fault occurs.
•These results show that the use of governors and excitation control can
improve significantly the electromechanical oscillations, damping and
the voltage stability of electric machines.

15. THE END
THANKS AND GOD BLESS